April 2012 Research E-News

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In this issue

Policy & Planning

MnPASS lanes improve travel time, safety

Researchers with the Humphrey School of Public Affairs and the Department of Civil Engineering have completed a benefit-cost analysis of the I-394 MnPASS program. MnPASS on I-394 consists of high-occupancy-toll (HOT) lanes between downtown Minneapolis and the city’s western suburbs.

In this study, the researchers evaluated the costs and net societal benefits of the project, including travel time savings, travel time reliability, and safety. Results confirm that the benefits from reduced congestion and increased safety far outweigh the capital and operating costs of the I-394 MnPASS lanes.

The research team included Humphrey School assistant professor Xinyu (Jason) Cao and senior fellow Lee Munnich, civil engineering associate professor Henry Liu, and graduate students Sean He, Zhiyi Xu, and Arthur Huang. The study was sponsored by the ITS Institute. 

The research team used dynamic toll records to estimate travel time and reliability savings for MnPASS drivers. Researchers computed travel time savings by comparing the difference between drivers traveling in the MnPASS lanes and those in the general lanes during the same time period.

The researchers also examined drivers’ value of travel time savings and travel time reliability. Results indicate that MnPASS users choose the HOT lanes because they value both travel time savings and reliability, with the value of overall reliability being almost three times larger than time savings. In fact, researchers said, the value of travel time reliability compensates for 23 percent of MnPASS costs, with benefits from travel time savings at only 7 percent.

Safety was the largest benefit of the MnPASS lanes, according the researchers. The lanes improve safety by attracting drivers, which allows traffic in the general lanes to flow more smoothly. The designated access and exit points to the HOT lanes help reduce sudden entries and exists, which lowers the risk of crashes. According to the researchers, overall traffic crashes were reduced by 5.3 percent after the HOT lanes were installed, resulting in an average economic benefit of more than $4.5 million per year.

Using this information, the researchers computed two benefit-cost ratios for MnPASS on I-394. One ratio considered only travel time savings, and the other included both time savings and reliability. Both demonstrated that MnPASS is economically justified, with the time and reliability cost-benefit ratio at 2.19 and the time-only ratio at 1.95.

Overall, the researchers say it is important to consider the benefits of travel time reliability as well as the effect of the HOT lanes on safety. Ignoring these factors could substantially understate MnPASS benefits. Future work could also consider the travel time benefits to drivers in general traffic lanes, since travel speeds increased in those lanes as well.

A final report on the project, Benefit and Cost Analysis of the I-394 MnPASS Program (CTS 12-30), is available on the ITS Institute website.

Intelligent Transportation Systems

Traffic management tools improve freeway performance

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In a study sponsored by the Minnesota Department of Transportation (MnDOT), researchers from the Department of Civil Engineering at the University of Minnesota Duluth have developed new tools to improve freeway management.

Professor Eil Kwon, director of the Northland Advanced Transportation Systems Research Laboratory, and researcher Chongmyung Park created tools to manage corridor performance, reduce bottlenecks, and monitor traffic trends. They also developed a system that combines MnDOT’s existing freeway traffic control system with microscopic simulation software to help managers develop and test new operational strategies.

The freeway network in the Twin Cities is currently managed with the Intelligent Road Information System (IRIS), MnDOT’s computerized operating system. IRIS is used to operate ramp meters, variable message signs, and loop detectors.

In this study, the researchers combined IRIS with microscopic simulation software, which allowed them to directly code new operational strategies into IRIS and evaluate them in a simulated environment. The resulting IRIS-in-Loop Simulation System (ILSS) makes it possible to develop and refine new operational strategies in realistic conditions before they are implemented in the field.

Other operational tools developed in the study include a computer program that estimates the performance of a freeway corridor using data from field detectors, a graphical overview showing the location of bottlenecks and their effects, and a process to assist traffic operators in monitoring daily traffic trends and identifying abnormal patterns. These tools can be used to support ongoing decisions about freeway planning and operations, including refinements to ramp metering, incident management, and travel time information systems.

The research team used the ILSS to assess a new variable speed limit (VSL) control strategy. The strategy is designed to mitigate shockwaves caused by downstream bottlenecks by gradually reducing the speed levels of incoming traffic. Preliminary results with microscopic simulation indicate that the VSL system could reduce the sudden deceleration rates caused by bottlenecks without substantially increasing travel times.

Kwon and Park also used ILSS to develop and evaluate an alternative ramp-metering algorithm. This new algorithm identifies bottlenecks for a given corridor every 30 seconds and determines appropriate metering rates for each entrance ramp depending on the estimated density of each road segment. The researchers simulated the new algorithm on segments of I-35W and Highway 169 and compared its performance with current IRIS metering control. Results indicate that the new algorithm can significantly reduce the amount of congestion compared to the existing metering method.

The researchers plan to field test the ramp-metering strategy on a selected corridor. Future work will also include enhancements to the VSL control algorithm to reflect weather conditions and reduce bottleneck identification time.

Development of Freeway Operational Strategies with IRIS-in-Loop Simulation (MnDOT 2012-04), a final report on the project, is available on the ITS Institute website.

CrashHelp pilot study demonstrates benefits, future needs

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In an ongoing effort to facilitate communication and improve patient care following traffic crashes, researchers with the Center for Excellence in Rural Safety (CERS) and the Intelligent Transportation Systems Institute have completed a pilot study of the prototype CrashHelp system.

CrashHelp is a smartphone-based system that enables emergency responders to collect multimedia data about crash victims on-scene and send it directly into emergency rooms, providing hospitals with advance notification of crash severity and related information that can be used to best prepare for a patient’s arrival.

Tom Horan, CERS research director, reviewed the results of the pilot study in a recent CERS webinar.  The study—conducted from July through October 2011 in Boise, Idaho—included participants from six hospitals and two ambulance providers.

During the pilot, ambulance crew paramedics and emergency medical technicians used a CrashHelp-equipped smartphone to securely capture pictures, digital audio recordings, video, and basic patient and incident information. The information was then sent to the participating hospital, where an automated phone call informed hospital personnel that new incident information was available for viewing on CrashHelp’s web-based interface. An acknowledgement was sent to the medic after the file had been accessed, and the medic could then send any additional information via text message.

A total of 801 incident transmittals were completed during the study period, including more than 400 images and nearly 450 audio recordings. Horan said the researchers had anticipated images being used most frequently and were surprised by the popularity of the audio recordings. The consistent use of audio could be because emergency responders are most comfortable with this type of reporting since they already provide verbal reports to emergency departments over the radio.

The researchers also found that use of the system varied widely between more technically savvy personnel and those who didn’t know how to make the best use of the system. “Moving forward, we see the need to do more training in order to get a full range of proficiency,” Horan said.

The team conducted follow-up focus groups with personnel from participating hospitals and ambulance providers, state EMS agencies, and the Idaho Department of Transportation. Overall results were positive, indicating that CrashHelp allowed for the efficient collection of usable information. Medics reported that seeing the information being used in hospitals drove them to make more use of the system, and hospital personnel said the information they received helped them prepare for a patient’s arrival—especially for those coming from farther away.

The study also helped the researchers identify future needs, such as protocol on how many and what types of pictures would provide the most value to emergency room personnel. There is also interest in additional notification types, such as an automated phone call that plays the available audio message automatically for hospital personnel.

Idaho has expressed interest in extending the pilot and expanding coverage to a rural area, Horan said. The researchers are also planning a pilot effort in St. Cloud, Minnesota, where they will investigate how CrashHelp could be used as part of a hospital-to-hospital referral system.

Watch the webcast

Transportation and the Environment

Seminar highlights costs and benefits of living snow fences

Heavy Equiptment

Blowing and drifting snow are costly realities for transportation agencies in regions with significant snowfall. Large, heavy drifts can require extra snowplow trips or the use of specialized removal equipment to keep roadways passable.

Living snow fences—plantings of trees, shrubs, or grasses set back from the right-of-way—can be used to minimize blowing and drifting problems on a roadway. The fences can also decrease travel time and reduce the number and severity of snow-related crashes.

Gary Wyatt, agroforestry professor at the University of Minnesota Extension, highlighted a benefit- and cost-analysis tool developed to help the Minnesota Department of Transportation (MnDOT) evaluate its living snow fence program at a February 21 CTS Research Seminar. The tool calculates the economic, transportation, and environmental benefits of the fences as well as the costs to landowners. The project was sponsored by MnDOT.

MnDOT has identified more than 3,700 snow problem areas in Minnesota using field survey data. Currently, living snow fence contracts with landowners are in place at only 2.3 percent of those sites.

The cost and benefit tool was designed to help transportation managers determine the feasibility of installing a living snow fence at these problem sites. The tool factors in the cost of snow and ice control, the safety benefits from reduced crashes and improved mobility, and the farmer or landowner cost of installing and maintaining a snow fence on private property. It generates a dollar figure for each cost and benefit area, helping officials determine which sites are the most cost-effective to target for future installations. This information can also be used to establish a fair payment amount to landowners to cover maintenance costs or lost crop yields.

Wyatt said that MnDOT could see net economic returns of more than $1.3 million per year if living snow fences were installed at 40 percent of the identified snow problem areas. At sites with superelevated curves, accidents could be reduced by up to 40 percent if living snow fences were implemented.

“This decision-making tool will help shape MnDOT’s blowing and drifting snow control program to save lives, save money, and save time for highway users now and into the future,” said Dan Gullickson, coordinator of MnDOT’s Living Snow Fence Program.

Although the tool has been tailored for MnDOT use, Wyatt said it could be used by other transportation agencies in the future. The current tool uses MnDOT-specific data on labor, equipment, and material costs, but other transportation officials at the state, county, and township level could enter information specific to their roadway system.

To learn more about the tool and its development, watch the seminar recording or download the full project report, Economic and Environmental Costs and Benefits of Living Snow Fences (MnDOT 2012-03), on the CTS website.

Transportation Infrastructure

New design procedures for unbonded concrete overlays

Unbonded concrete overlays (UBCOs) are becoming increasingly popular for highway pavement rehabilitation. They are cost-effective, durable, and capable of restoring ride quality and structural capacity to existing deteriorated pavements. However, most current design methods are based on empirical equations or simplified mechanistic models, and none have been universally accepted.

In a study sponsored by the Minnesota Department of Transportation (MnDOT), civil engineering professor Roberto Ballarini and graduate student Minmao Liao developed new UBCO design procedures based on fracture mechanics principles. These new procedures have the potential to make UBCOs more resistant to reflection cracking and other potential loading conditions.

UBCO systems consist of a portland cement concrete (PCC) overlay that is separated from an original, damaged PCC pavement by a thin asphalt concrete interlayer. The interlayer is typically one to two inches thick and is designed to prevent reflection cracking in the overlay. In Minnesota, UBCOs are constructed so that the combination of the existing pavement and the overlay is the structural equivalent of a new single-layer PCC pavement.

To develop a fracture-mechanics-based approach for designing UBCOs, the researchers began by analyzing a single-layer pavement for reference. They examined the relationships between the ultimate load capacity, material properties, and geometry of the single-layer pavement. They then completed a two-dimensional model of an UBCO system, including the dimensions and material properties of the overlay and the interlayer. Using this information, the research team developed equations for the load-carrying capacity of an UBCO system.

The researchers then compared the results of the model with observations from a field study of UBCOs at the MnROAD research facility in Monticello, Minnesota. Four thin UBCO sections implemented at MnROAD showed no signs of cracking except near the joints separating the test cells. This suggests that thinner UBCOs are capable of resisting potential reflection cracking, the researchers say. The thicker overlays that would have been chosen using currently available design procedures would have been overly conservative.

The researchers suggest conducting further research to assess the accuracy of the model predictions. They would also like to conduct additional experiments and consider other three-dimensional fracture mechanics simulations to provide addition information on the most cost-effective UBCO design.

The final project report, Mechanistic Modeling of Unbonded Concrete Overlay Pavements (MnDOT 2012-02), is available on the CTS website.

Transit, Bicycling, and Walking

TCRP research publications available online

The federal Transit Cooperative Research Program (TCRP), administered by the Transportation Research Board, provides practical transit research to address technical and operational issues. TCRP emphasizes putting research results into the hands of organizations and individuals that can use them to solve problems.

Recent TCRP publications include:

Upcoming Events

April 24-26
National Transportation Workforce Summit, Washington, D.C.

April 29-May 1
IBTTA Symposium on Mileage-Based User Fees and Transportation Finance Summit, Jersey City, New Jersey

May 23-24
23rd Annual CTS Transportation Research Conference, Saint Paul RiverCentre, St. Paul, MN